A polyurethane resin is a resin having excellent strength, flexibility, wear resistance, and oil resistance, and is widely used as a resin for paints and adhesives. In recent years, a polyhydroxyurethane resin having a urethane bond and a hydroxy group together in the chemical structure thereof has been developed as a novel polyurethane-based resin, and industrial applications thereof are expected (see Patent Literature 1). Existing polyurethane resins are obtained using an isocyanate compound and a polyol as raw materials, while the polyhydroxyurethane resin is produced using an epoxy compound, carbon dioxide, and an amine compound as raw materials and combining these raw materials. Carbon dioxide used as a raw material is incorporated into the chemical structure of the polyhydroxyurethane resin as a —CO—O— bond, and therefore the polyhydroxyurethane resin is a resin material to which attention should be paid also from the viewpoint of effective utilization of carbon dioxide being a greenhouse gas.
The polyhydroxyurethane resin as well as the existing polyurethane resins can be made into a resin having excellent mechanical properties, and further, applications making the best use of functionalities derived from a hydroxy group which does not exist in the structures of the existing polyurethane resins have been studied. For example, an application as a heat-resistant paint utilizing crosslinking reaction of the hydroxy group (see Patent Literature 2) and an application to a gas-barrier film utilizing a gas-barrier property derived from the hydroxy group have been studied (see Patent Literature 3).
As found in these conventional techniques, the field of paints and the field of coating are promising as the application use of polyhydroxyurethane resins. However, polyhydroxyurethane resins which have so far been developed each contain a chemical structure having a hydroxy group together with a urethane bond and therefore have a low solubility to organic solvents, so that there are many cases where the solubility is different depending on the base material and the processing apparatus used in each use and there has been a problem in practical use in that it is difficult to adapt a polyhydroxyurethane resin to various solvent compositions. To deal with this problem, making a polyhydroxyurethane resin into an aqueous dispersion, thereby solving this problem, and applying the polyhydroxyurethane resin to water-based paints, with which solvent-based paints have been replaced in recent years, have been studied and are proposed (see Patent Literature 4). In addition, as another method, a method for obtaining a polyhydroxyurethane resin having a carboxyl group using a carboxylic acid-containing amine compound as a raw material is proposed (see Patent Literature 5).
In addition, as a method for improving the gas-barrier property of a polyhydroxyurethane resin, a method for making a composite with a clay mineral is proposed (Patent Literature 6). Generally, to disperse a clay mineral in a resin, a hydrophobization treatment such as replacing an interlayer metal cationic ion with an organic onium salt is needed, and in the conventional techniques described above, a clay mineral is subjected to a hydrophobization treatment and is thereafter made into a composite.